Synthesis and Biologic Evaluation of an Iodine-Labeled Entecavir Derivative for Anti-hepatitis B Virus Activity

To label entecavir (ETV) with radioiodine and evaluate its effect on inhibiting hepatitis B virus (HBV) secretion and replication in vitro as well as its biodistribution in BALB/c mice.

¹²⁵I-ETV was synthesized via binding a vinyl tributyltin group to ETV and producing electrophilic iodination of the group. Its chemical properties were assessed using traditional methods. Upon intravenous injection of ¹²⁵I-ETV into BALB/c mice, the radioactivity of the critical organs was detected. In vitro, the anti-HBV activity of ¹²⁵I-ETV was investigated using HepG2.2.15 cell culture model. Confocal microscopy was used to analyze the cell apoptosis. Culture supernatant samples were used for measuring HBV surface antigen (HBsAg) and HBV e antigen (HBeAg) by enzyme-linked immunosorbent assay. Intracellular HBV pregenomic RNA (pgRNA), DNA, and covalently closed circular DNA (cccDNA) were measured by real-time fluorescence quantitative PCR.

The radiochemical purity of ¹²⁵I-ETV was greater than 95% after incubation in freshly serum within 48 h. The three highest radioactivities were in the stomach, intestine, and liver after intravenous injection at 0.5 h, 2 h, and 24 h. The confocal fluorescence imaging showed that ¹²⁵I-ETV did not induce cell apoptosis after treatment for 96 h. ¹²⁵I-ETV decreases HBsAg and HBeAg secretions as well as intracellular HBV pgRNA, DNA, and cccDNA copies in a dose-dependent manner. Moreover, the anti-HBV activity of ¹²⁵I-ETV is greater than that of ETV.

The study outcome establishes ¹²⁵I-ETV as a candidate for anti-HBV. However, it is still in need of further endorsement and optimization by animal model studies before using ¹²⁵I-ETV to treat chronic HBV disease.